The present invention is directed to dry toner compositions suitable for the development of electrostatic images. More specifically, the present invention is directed to dry toner compositions containing colored silica particles and polymers with at least two different blocks or segments. One embodiment of the present invention is directed to a dry toner composition comprising a resin, hydrophilic silica particles having dyes covalently bonded to the particle surfaces through silane coupling agents, and a polymer having at least one segment capable of adsorbing onto the surface of the silica particles and at least one segment capable of enhancing the dispersability of the silica particles in the resin. In another embodiment of the present invention, one segment of the polymer is ionophoric and capable of complexing with a salt, thereby imparting charge control agent properties to the composition.
The formation and development of images on the surface of photoconductive materials by electrostatic means is well known. The basic electrophotographic imaging process, as taught by C. F. Carlson in U.S. Pat. No. 2,297,691, entails placing a uniform electrostatic charge on a photoconductive insulating layer known as a photoconductor or photoreceptor, exposing the photoreceptor to a light and shadow image to dissipate the charge on the areas of the photoreceptor exposed to the light, and developing the resulting electrostatic latent image by depositing on the image a finely divided electroscopic material known as toner. The toner will normally be attracted to those areas of the photoreceptor which retain a charge, thereby forming a toner image corresponding to the electrostatic latent image. This developed image may then be transferred to a substrate such as paper. The transferred image may subsequently be permanently affixed to the substrate by heat, pressure, a combination of heat and pressure, or other suitable fixing means such as solvent or overcoating treatment.
Electrophotographic processes can be employed to form colored images. For example, the formation of highlight color images, wherein documents are generated containing separate image areas of two or more different colors, is well known. In addition, the formation of full color images, wherein documents are generated containing full color images by sequentially forming and developing images with cyan, magenta, yellow, and optionally black toners, is well known. High quality color toners are desirable for both applications, and toners with a high degree of transparency and good color mixing are particularly desirable for full color copying and printing processes. Transparent colored toners, by which is meant colored toners in which light scattering is minimized as light passes through images developed with the toners, are generally obtained either by employing a dye molecularly dispersed in the toner resin as a colorant or by employing very finely divided pigment particles, generally with an average particle diameter of about 50 nanometers or less, uniformly dispersed in the toner resin as a colorant.
Electrophotographic toners containing colored silica particles are known. For example, U.S. Pat. No. 4,566,908 discloses an azoic pigment suitable for use in an electrophotographic toner having a silica core comprising a core of a fine powder of silica having a particle diameter of not more than 10 microns and a coating of a mono- or polyazoic dye chemically bound to the surface of the silica core through an aminosilane coupling agent. The process for preparing these colored silica particles is detailed at columns 8 to 18 of the patent. In addition, U.S. Pat. No. 4,576,888 discloses a toner for electrophotography comprising an azoic pigment having a silica core as a coloring component, the azoic pigment comprising a core of a fine powder of silica and a coating of a mono- or polyazoic dye chemically bound to the surface of the silica core through an aminosilane coupling agent. Further, R. Ledger and E. Stellwagen, "Preparation and Analysis of Reactive Blue 2 Bonded to Silica Via Variable Spacer Groups," Journal of Chromatography, vol. 299, pages 175 to 183 ( 1984), discloses processes for preparing colored silica particles by covalently attaching Reactive Blue 2 dye to silica particles through various spacer groups. The disclosure of this article is totally incorporated herein by reference.
Additionally, U.S. Pat. No. 3,290,165 discloses processes for preparing finely divided particulate inorganic pigments modified with amino organosilanes. The modified pigments are suitable for use as fillers for thermosetting resins or as fillers for paper, paints, varnishes, inks, and paper coating compositions. The modified pigments can also be dyed with direct dyes for use as color-imparting fillers. Further, U.S. Pat. No. 3,834,924 discloses a process for producing surface modified finely divided inorganic pigments by addition of an organosilane to a high solids content aqueous dispersion of an inorganic pigment in a mixing apparatus to yield a thick, flowable plastic-type mass suitable for extrusion and drying.
Further, U.S. Pat. No. 4,592,989, the disclosure of which is totally incorporated herein by reference, discloses a toner comprising resin particles, pigment particles, and a complex of a dipolar molecule or salt attached to an ionophoric polymer. The ionophoric polymer can be a polyether diblock copolymer, such as styrene/ethylene oxide diblock polymers.
In addition, U.S. Pat. No. 4,680,200 discloses a process for preparing a colloidal size particulate wherein colloidal size particles of an organic solid such as a pigment are encapsulated in a hydrophobic addition polymer, such as a polymer of styrene, by a polymerization addition process wherein a water-immiscible (hydrophobic) monomer is dispersed in an aqueous colloidal dispersion of the organic particles and subjected to conditions of emulsion polymerization. The resulting encapsulated particles are useful in toners and as pigments.
U.S. Pat. No. 4,681,829 discloses a positively charged single component toner comprising resin particles, monoazo or substituted perylene pigment particles, and a charge enhancing additive, as well as additive particles such as colloidal silica or low molecular weight waxes. In addition, U.S. Pat. No. 4,820,604 discloses a toner comprising resin particles, pigment particles, and a sulfur containing organopolysiloxane wax.
Additionally, U.S. Pat. No. 4,877,451, the disclosure of which is totally incorporated herein by reference, discloses ink jet inks comprising water, a solvent, and a plurality of colored particles comprising hydrophilic silica particles to the surfaces of which dyes are covalently bound through silane coupling agents. In addition, of background interest are U.S. Pat. No. 2,876,119; U.S. Pat. No. 2,993,809; U.S. Pat. No. 3,939,087; U.S. Pat. No. 4,179,537 and U.S. Pat. No. 4,204,871.
Copending application U.S. Ser. No. 07/369,003 entitled "Inks and Liquid Developers Containing Colored Silica Particles," with the named inventors Francoise M. Winnik, Barkev Keoshkerian, Raymond W. Wong, Stephan Drappel, Melvin D. Croucher, James D. Mayo, and Peter G. Hofstra, discloses ink jet inks comprising a liquid medium and a plurality of colored silica particles and liquid electrophotographic developers comprising a liquid medium, a charge control agent, a resin, and a plurality of colored silica particles.
It has been observed that while colored hydrophilic silica particles disperse well in hydrophilic resins, such as polyvinylpyrrolidinone or polyvinyl alcohol, they tend to disperse poorly and aggregate irreversibly in typical toner resins, such as polyester resins, styrene-butadiene resins, styrene-acrylate and styrene-methacrylate resins, and the like. Resins such as polyvinylpyrrolidinone or polyvinyl alcohol, however, typically are not selected as toner resins because they are hydrophilic and their triboelectric properties may change significantly with changes in ambient relative humidity. These resins also can exhibit considerable hydrogen bonding, which may adversely affect melt flow characteristics. Further, hydrophilic resins such as polyvinylpyrrolidinone and the like generally do not exhibit physical and rheological properties usually desired for toner resins, and may be difficult to process into toners by conventional methods such as extrusion and attrition. Accordingly, although the above described compositions and processes are suitable for their intended purposes, a need continues to exist for dry electrophotographic toners available in a wide variety of colors. In addition, a need continues to exist for simple and economical processes for preparing colored particles suitable for dry electrophotographic toners. Further, there is a need for dry toner compositions wherein the particle size and particle size distribution of the colorant particles can be well controlled. There is also a need for dry colored toner compositions with a high degree of transparency, thereby enhancing color quality and enabling the formation of high quality full color images by sequentially applying images of primary colors to a single substrate, each successive image being applied on top of the previous image. A further need exists for dry colored toner compositions containing colored silica particles that are uniformly dispersed in the toner resin. In addition, there is a need for dry colored toner compositions containing silica particle colorants wherein a polymer-salt complex adsorbed onto the silica particles functions as a charge control agent. A need also exists for dry colored toner compositions containing mixtures of silica particles of two or more different colors, resulting in a toner of a desired color. Also, there is a need for dry toner compositions with colorants of low toxicity. There is a further need for dry toner compositions with silica particle colorants of relatively small particle size wherein the silica particles are well dispersed in the resin with minimal or no particle agglomeration, thereby resulting in enhanced toner transparency and color quality.